byVal Vs. byRef

[Rob Panosh]

Hello,

Ok here is the senerio:

.....

Dim myArrayList as New ArrayList(0)

me.Test_A( myArrayList )

myArralist.Coun t > 0 'This will be TRUE.

Public Sub Test_A( byVal X as ArrayList )

'Add three items.
X.Add( "Item 1")
X.Add( "Item 2")
X.Add( "Item 3")

RETURN
When should I make the incoming parameter X as byRef?
Thanks,
Rob Panosh

[William Ryan]

Rob:

I'm not sure what you are asking, but an ArrayList is a Reference type, so
even if you pass it by value, all you are passing is a Copy of the REFERENCE
to the object. For all intents and purposes you won't notice the
difference. Yes, if you pass this reference type ByVal and the function
it's passed to makes any changes to it, the original ArrayList will be
changed. So the only difference between passing a Ref type byval or byRef
is that in the first case you pass a copy of the Reference, in the second
you pass the actual reference. If you want a unique copy that you can do
with what you please, you'll probalby need to opt for a deep clone of it.

HTH,

Bill
"Rob Panosh" <ro************ ************@as dsoftadfdware.c om> wrote in
message news:Om******** *****@TK2MSFTNG P11.phx.gbl...

Hello,

Ok here is the senerio:

....

Dim myArrayList as New ArrayList(0)

me.Test_A( myArrayList )

myArralist.Coun t > 0 'This will be TRUE.

Public Sub Test_A( byVal X as ArrayList )

'Add three items.
X.Add( "Item 1")
X.Add( "Item 2")
X.Add( "Item 3")

RETURN
When should I make the incoming parameter X as byRef?
Thanks,
Rob Panosh

[Brian Henry]

that should be a byref if you are going to make changes to it that will be
visible outside of that sub... byval only makes a copy of the data.. byref
makes a pointer to the data, which is what you need if you are going to make
changes that are visible outside of that test sub, or they will just get
thrown out as the sub exits... and why do you have return in there?
"Rob Panosh" <ro************ ************@as dsoftadfdware.c om> wrote in
message news:Om******** *****@TK2MSFTNG P11.phx.gbl...

Hello,

Ok here is the senerio:

....

Dim myArrayList as New ArrayList(0)

me.Test_A( myArrayList )

myArralist.Coun t > 0 'This will be TRUE.

Public Sub Test_A( byVal X as ArrayList )

'Add three items.
X.Add( "Item 1")
X.Add( "Item 2")
X.Add( "Item 3")

RETURN
When should I make the incoming parameter X as byRef?
Thanks,
Rob Panosh

[Rob Panosh]

William,

even if you pass it by value, all you are passing is a Copy of the REFERENCE to the object. That is what I was asking. I could see a difference between them. So are
there any peformance implications here?
My guess byRef would have better performance because it doesn't have to make
a copied of the reference.

Thanks for your help and timely reponse

Rob
"William Ryan" <do********@com cast.nospam.net > wrote in message
news:uS******** ******@TK2MSFTN GP09.phx.gbl... Rob:

I'm not sure what you are asking, but an ArrayList is a Reference type, so
even if you pass it by value, all you are passing is a Copy of the REFERENCE to the object. For all intents and purposes you won't notice the
difference. Yes, if you pass this reference type ByVal and the function
it's passed to makes any changes to it, the original ArrayList will be
changed. So the only difference between passing a Ref type byval or byRef
is that in the first case you pass a copy of the Reference, in the second
you pass the actual reference. If you want a unique copy that you can do
with what you please, you'll probalby need to opt for a deep clone of it.

HTH,

Bill
"Rob Panosh" <ro************ ************@as dsoftadfdware.c om> wrote in
message news:Om******** *****@TK2MSFTNG P11.phx.gbl...

Hello,

Ok here is the senerio:

....

Dim myArrayList as New ArrayList(0)

me.Test_A( myArrayList )

myArralist.Coun t > 0 'This will be TRUE.

Public Sub Test_A( byVal X as ArrayList )

'Add three items.
X.Add( "Item 1")
X.Add( "Item 2")
X.Add( "Item 3")

RETURN
When should I make the incoming parameter X as byRef?
Thanks,
Rob Panosh

[Rob Panosh]

> that should be a byref if you are going to make changes to it that will be
It doesn't make any difference how I pass it I can still see the changes.

thrown out as the sub exits... and why do you have return in there? fat fingers .... didn't mean to put it there.

rob

"Brian Henry" <brianiup[nospam]@adelphia.net> wrote in message
news:e4******** ******@TK2MSFTN GP11.phx.gbl... that should be a byref if you are going to make changes to it that will be
visible outside of that sub... byval only makes a copy of the data.. byref
makes a pointer to the data, which is what you need if you are going to make changes that are visible outside of that test sub, or they will just get
thrown out as the sub exits... and why do you have return in there?
"Rob Panosh" <ro************ ************@as dsoftadfdware.c om> wrote in
message news:Om******** *****@TK2MSFTNG P11.phx.gbl...

Hello,

Ok here is the senerio:

....

Dim myArrayList as New ArrayList(0)

me.Test_A( myArrayList )

myArralist.Coun t > 0 'This will be TRUE.

Public Sub Test_A( byVal X as ArrayList )

'Add three items.
X.Add( "Item 1")
X.Add( "Item 2")
X.Add( "Item 3")

RETURN
When should I make the incoming parameter X as byRef?
Thanks,
Rob Panosh

[Glen Conway]

Rob,

If Test_A was function and you were assigning an array list back to
myArrayList then ByVal is OK. If it's a sub and you want the original
object modified then pass it as ByRef. In this instance, Test_A only
creates a new ArrayList object (X), adds some items and then does nothing,
myArrayList isn't modified at all.

Hope this helps

Glen

"Rob Panosh" <ro************ ************@as dsoftadfdware.c om> wrote in
message news:Om******** *****@TK2MSFTNG P11.phx.gbl...

Hello,

Ok here is the senerio:

....

Dim myArrayList as New ArrayList(0)

me.Test_A( myArrayList )

myArralist.Coun t > 0 'This will be TRUE.

Public Sub Test_A( byVal X as ArrayList )

'Add three items.
X.Add( "Item 1")
X.Add( "Item 2")
X.Add( "Item 3")

RETURN
When should I make the incoming parameter X as byRef?
Thanks,
Rob Panosh

[Rob Panosh]

William,

even if you pass it by value, all you are passing is a Copy of the REFERENCE to the object. That is what I was asking. I could see a difference between them. So are
there any peformance implications here?
My guess byRef would have better performance because it doesn't have to make
a copied of the reference.

Thanks for your help and timely reponse

Rob
"William Ryan" <do********@com cast.nospam.net > wrote in message
news:uS******** ******@TK2MSFTN GP09.phx.gbl... Rob:

I'm not sure what you are asking, but an ArrayList is a Reference type, so
even if you pass it by value, all you are passing is a Copy of the REFERENCE to the object. For all intents and purposes you won't notice the
difference. Yes, if you pass this reference type ByVal and the function
it's passed to makes any changes to it, the original ArrayList will be
changed. So the only difference between passing a Ref type byval or byRef
is that in the first case you pass a copy of the Reference, in the second
you pass the actual reference. If you want a unique copy that you can do
with what you please, you'll probalby need to opt for a deep clone of it.

HTH,

Bill
"Rob Panosh" <ro************ ************@as dsoftadfdware.c om> wrote in
message news:Om******** *****@TK2MSFTNG P11.phx.gbl...

Hello,

Ok here is the senerio:

....

Dim myArrayList as New ArrayList(0)

me.Test_A( myArrayList )

myArralist.Coun t > 0 'This will be TRUE.

Public Sub Test_A( byVal X as ArrayList )

'Add three items.
X.Add( "Item 1")
X.Add( "Item 2")
X.Add( "Item 3")

RETURN
When should I make the incoming parameter X as byRef?
Thanks,
Rob Panosh

[Rob Panosh]

> that should be a byref if you are going to make changes to it that will be
It doesn't make any difference how I pass it I can still see the changes.

thrown out as the sub exits... and why do you have return in there? fat fingers .... didn't mean to put it there.

rob

"Brian Henry" <brianiup[nospam]@adelphia.net> wrote in message
news:e4******** ******@TK2MSFTN GP11.phx.gbl... that should be a byref if you are going to make changes to it that will be
visible outside of that sub... byval only makes a copy of the data.. byref
makes a pointer to the data, which is what you need if you are going to make changes that are visible outside of that test sub, or they will just get
thrown out as the sub exits... and why do you have return in there?
"Rob Panosh" <ro************ ************@as dsoftadfdware.c om> wrote in
message news:Om******** *****@TK2MSFTNG P11.phx.gbl...

Hello,

Ok here is the senerio:

....

Dim myArrayList as New ArrayList(0)

me.Test_A( myArrayList )

myArralist.Coun t > 0 'This will be TRUE.

Public Sub Test_A( byVal X as ArrayList )

'Add three items.
X.Add( "Item 1")
X.Add( "Item 2")
X.Add( "Item 3")

RETURN
When should I make the incoming parameter X as byRef?
Thanks,
Rob Panosh

[Glen Conway]

Rob,

If Test_A was function and you were assigning an array list back to
myArrayList then ByVal is OK. If it's a sub and you want the original
object modified then pass it as ByRef. In this instance, Test_A only
creates a new ArrayList object (X), adds some items and then does nothing,
myArrayList isn't modified at all.

Hope this helps

Glen

"Rob Panosh" <ro************ ************@as dsoftadfdware.c om> wrote in
message news:Om******** *****@TK2MSFTNG P11.phx.gbl...

Hello,

Ok here is the senerio:

....

Dim myArrayList as New ArrayList(0)

me.Test_A( myArrayList )

myArralist.Coun t > 0 'This will be TRUE.

Public Sub Test_A( byVal X as ArrayList )

'Add three items.
X.Add( "Item 1")
X.Add( "Item 2")
X.Add( "Item 3")

RETURN
When should I make the incoming parameter X as byRef?
Thanks,
Rob Panosh

[Jay B. Harlow [MVP - Outlook]]

Rob,
In addition to the others comments:

When should I make the incoming parameter X as byRef? Short answer: Only when you need to modify the caller's variable!

Long answer:
ByVal & ByRef Parameters are independent of Reference & Value Types. All
parameters by default are passed ByVal, you should only pass a parameter
ByRef when you have to, which is when you need to modify the callers
variable.

Less memory use & better performance should not be a factor in choosing
ByVal & ByRef. The only time to consider ByRef for less memory & performance
is when passing large structures (structures as in defined with the
Structure keyword), however structures should never be large!

Structure Usage Guidelines.
http://msdn.microsoft.com/library/de...guidelines.asp

A Reference Type is an object that exists on the heap. If I have a variable
that is a reference type and assign the variable to another variable. Both
variables will be pointing to the same object on the heap.

Dim x As Person
x = New Person()
Dim y As Person
y = x

Both x & y are the exact same Person object on the heap.

A Value Type does not live on the Heap. If I have a value type variable and
I assign it to another variable, a copy of the value is made.

Dim x As Integer
x = 100
Dim y As Integer
y = x

Although both x & y have the value 100, they are physically different values
as a copy was made.

Now when you pass a variable to a ByVal parameter a copy of the variable is
made. So for a Reference Type a copy of the reference is made, which means
there is still only one object on the heap & two references to that object.
For a Value Type a copy of the value is made.

When you pass a variable to a ByRef parameter a reference to that variable
is made. So for a Reference Type you have a reference to a reference to the
object, for a Value Type you have a reference to the value.

Remember ByVal & ByRef are how parameters are passed. Reference & Value
Types are how quantities are stored.

Hope this helps
Jay

"Rob Panosh" <ro************ ************@as dsoftadfdware.c om> wrote in
message news:Om******** *****@TK2MSFTNG P11.phx.gbl... Hello,

Ok here is the senerio:

....

Dim myArrayList as New ArrayList(0)

me.Test_A( myArrayList )

myArralist.Coun t > 0 'This will be TRUE.

Public Sub Test_A( byVal X as ArrayList )

'Add three items.
X.Add( "Item 1")
X.Add( "Item 2")
X.Add( "Item 3")

RETURN
When should I make the incoming parameter X as byRef?
Thanks,
Rob Panosh